1. Field of the Invention
The present invention is directed to the field of image forming devices having a sensor for indicating toner level, and more particularly to a toner container structure and system for an image forming apparatus and method for assessing toner consumption as measured by the number of pixels printed by the image forming apparatus.
2. Description of the Related Art
Image forming devices including copiers, laser printers, facsimile machines, and the like, include a photoconductive drum having a rigid cylindrical surface that is coated along a defined length of its outer surface. The surface of the drum is charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. The areas of the drum surface exposed to light are discharged and form a latent electrostatic image on the drum surface. A developer material, such as toner having an electrical charge, is attracted to the photoconductive drum surface and is used for forming the image. The toner is stored in a reservoir adjacent to the photoconductive drum and is transferred to the drum by the developer roll. The thickness of the toner layer on the developer roll is controlled by a nip, which is formed between the doctor blade and the developer roll. A recording sheet, such as a blank sheet of paper, is then brought into contact with the discharged photoconductive drum surface and the toner thereon is transferred to the recording sheet in the form of the latent electrostatic image. The recording sheet is then heated to permanently fuse the toner to the sheet.
Additional background information may be found by reference to U.S. Pat. No. 6,510,291 to Campbell et al, hereinafter referred to as the '291 patent, the entire teachings and contents of which are incorporated herein by reference.
Laser printers often include gas gages that indicate how much toner remains in the toner cartridges. Various existing methods to estimate how much toner has been consumed include optical, capacitive, torque-based, weight-based, vibration-based, and others. An inexpensive method simply counts the dots that the laser printer prints (pixels) and estimates the toner consumption from the pixels printed. The original toner minus the amount used to print the pixels indicates the amount of remaining toner. Though inexpensive, this pixel-counting method is highly inaccurate. The pixel counting itself can have errors if the printer uses complex algorithms to place sub-pixels on adjacent lines to smooth images. Also, the amount of toner consumed by any given pixel is not a constant, and is affected by variables such as temperature, humidity, wear of components, and manufacturing tolerances of components. Further, adjacent pixels may consume different amounts of toner, so the toner consumption is affected by what is printed, not just by the number of printed pixels.
Of the various algorithms that have been proposed to account for all variations in toner consumption by a pixel, most are complex and inaccurate. An inaccurate estimate of toner consumption per pixel inevitably leads to an inaccurate estimate of remaining toner cartridge life and possible premature toner depletion.
There is, therefore, a need for a toner container structure and method for accurately assessing toner level based on the number of printed pixels.